Electric power steering unit

An electric power steering unit comprising a rack-shaft to be coupled to the guiding wheels of a vehicle, an electric motor coaxially arranged around the rack-shaft to supply assisting power to the rack-shaft, a ball screw mechanism for connecting a nut section linked to the armature shaft of the electric motor with a screw section formed on the rack-shaft by disposing ball members therebetween and for transmitting the rotary power of the electric motor to the rack-shaft as assisting power for steering, and a housing comprising a bearing for rotatably supporting said ball screw mechanism, characterized in that:

• said bearing comprises an outer ring pressed and fixed in an axial direction in said housing by a pre-load pressure member, and a rolling member which is provided between said outer ring and said nut section of said ball screw mechanism with the rolling member directly contacting the nut section, and the nut section has a ball circulation passageway with a radially outermost portion and also has a radially outer portion extending radially outwardly from the radially outermost portion of the circulation passageway, the rolling member being in angular contact with the outer portion of the nut section radially outwardly from the radially outermost portion of the circulation passageway so that an axially directed component of force applied by the rolling member to the nut section is located radially outwardly of the radially outermost portion of the circulation passageway so that a pressure force applied to said outer ring is not applied to the circulation passageway of the ball screw mechanism.

An electric power steering unit comprising a rack-shaft to be coupled to the guiding wheels of a vehicle, an electric motor coaxially arranged around the rack-shaft to supply assisting power to the rack-shaft, a ball screw mechanism for connecting a nut section linked to the armature shaft of the electric motor with a screw section formed on the rack-shaft by disposing ball members therebetween and for transmitting the rotary power of the electric motor to the rack-shaft as assisting power for steering, and a housing comprising a bearing for rotatably supporting said ball screw mechanism, characterized in that:

• said bearing comprises an outer ring pressed and fixed in an axial direction in the housing by a pre-load pressure member, an inner ring fixed to a corner of said nut section of said ball screw mechanism, and a rolling member provided between said outer ring and said inner ring and in angular contact with both said outer ring and said inner ring, and the nut section has a ball circulation passageway with a radially outermost portion and also has a radially outer portion extending radially outwardly from the radially outermost portion of the circulation passageway, the inner ring being in contact with the outer portion of the nut section radially outwardly from the radially outermost portion of the circulation passageway so that an axially directed component of force applied by the rolling member to the inner ring is located radially outwardly of the radially outermost portion of the circulation passageway so that a stress is not caused at a ball member of said ball screw mechanism by a pressure force applied to said outer ring.

An electric power steering unit comprising a rack-shaft to be coupled to the guiding wheels of a vehicle, an electric motor coaxially arranged around the rack-shaft to supply assisting power to the rack-shaft, a ball screw mechanism for connecting a nut section linked to the armature shaft of the electric motor with a screw section formed on the rack-shaft by disposing ball members therebetween and for transmitting the rotary power of the electric motor to the rack-shaft as assisting power for steering, and a housing comprising a bearing for rotatably supporting said ball screw mechanism, characterized in that:

• said bearing comprises an outer ring pressed and fixed in an axial direction in said housing by a pre-load pressure member, an inner ring fixed to a corner of said nut section of said ball screw mechanism, and a rolling member provided between said outer ring and said inner ring and in angular contact with both said outer ring and said inner ring, and the nut section has a ball circulation passageway with a radially outermost portion and also has a radially outer portion extending radially outwardly from the radially outermost portion of the circulation passageway, the inner ring being in contact with the outer portion of the nut section radially outwardly from the radially outermost portion of the circulation passageway so that an axially directed component of force applied by the rolling member to the inner ring is located radially outwardly of the radially outermost portion of the circulation passageway so that a pressure force applied to said outer ring is not applied to a circulation passageway.